Synchronizing motors for an electric propulsion system

Abstract

An electric propulsion system is described that includes an AC drive circuit, a synchronization circuit, and a control unit. The AC drive circuit includes a plurality of propulsor motors, an AC power bus, and an AC generator that delivers AC electrical power to the AC power bus for simultaneously driving the plurality of propulsor motors. The synchronization circuit is configured to synchronize, with the AC generator, single propulsor motor from the plurality of propulsor motors, at a time. The control unit is configured to maintain synchronicity between the single propulsor motor and the AC generator by engaging the synchronization circuit with the single propulsor motor in response to determining that the single propulsor motor is not synchronized with the AC generator.

What is claimed is: 
     
       1. An electric propulsion system comprising:
 an AC drive circuit that includes:
 a plurality of propulsor motors; 
 an AC power bus; and 
 an AC generator that delivers AC electrical power to the AC power bus for simultaneously driving the plurality of propulsor motors; 
 
 a synchronization circuit configured to individually synchronize, with the AC generator, a single propulsor motor from the plurality of propulsor motors, one at a time; and 
 a control unit configured to:
 determine whether the single propulsor motor is not synchronized with the AC generator; and 
 maintain synchronicity between the single propulsor motor and the AC generator by engaging the synchronization circuit with the single propulsor motor in response to determining that the single propulsor motor is not synchronized with the AC generator. 
 
 
     
     
       2. The electric propulsion system of  claim 1 , wherein the synchronization circuit is configured to synchronize the single propulsor motor with the AC generator by outputting synchronizing electrical power, that is derived from the AC electrical power delivered by the AC generator, to the single propulsor motor for driving the single propulsor motor in-phase with the AC generator. 
     
     
       3. The electric propulsion system of  claim 2 , wherein the synchronization circuit is configured to synchronize the single propulsor motor with the AC generator by refraining from outputting the synchronizing electrical power in response to determining the single propulsor motor is operating at a speed that satisfies an operating speed threshold. 
     
     
       4. The electric propulsion system of  claim 2 , wherein the synchronization circuit is further configured to synchronize the single propulsor motor with the AC generator by refraining from outputting synchronizing electrical power to each of the plurality of propulsor motors, other than the single propulsor motor. 
     
     
       5. The electric propulsion system of  claim 1 , wherein the synchronization circuit is configured to synchronize the single propulsor motor with the AC generator by adjusting, with the synchronizing electrical power, a frequency of the propulsor motor to be within a tolerance threshold of a frequency of the AC electrical power delivered by the AC generator. 
     
     
       6. The electric propulsion system of  claim 1 , wherein the synchronization circuit is configured to synchronize the single propulsor motor with the AC generator by adjusting, with the synchronizing electrical power, a phase shift of the propulsor motor to be within a tolerance threshold of a frequency of the AC electrical power delivered by the AC generator. 
     
     
       7. The electric propulsion system of  claim 1 , wherein the synchronization circuit is configured to synchronize the single propulsor motor with the AC generator by adjusting, with the synchronizing electrical power, a voltage of the propulsor motor to be within a tolerance threshold of a voltage associated with the AC generator. 
     
     
       8. The electric propulsion system of  claim 1 , wherein the synchronization circuit comprises a DC link circuit that includes a rectifier and an inverter, wherein the rectifier is configured to provide a DC electrical signal, based on the AC electrical power delivered by the AC generator, to the inverter, and the inverter is configured to output synchronizing electrical power, based on the DC electrical signal received from the rectifier or based on the AC bus, for driving the single propulsor motor in-phase with the AC generator. 
     
     
       9. The electric propulsion system of  claim 8 , further comprising a distributed propulsion system,
 wherein the AC generator comprises a shaft driven by an engine, and 
 wherein the DC link circuit further comprises an energy source for synchronizing the DC electrical signal during potential loss conditions associated with the AC electrical power being delivered by the AC generator. 
 
     
     
       10. The electric propulsion system of  claim 1 , wherein the AC drive circuit further includes a plurality of isolation devices that are configurable by the control unit to:
 electrically isolate the AC generator from the single propulsor motor while the synchronization circuit synchronizes the single propulsor motor with the AC generator; and 
 electrically couple the AC generator to each of the plurality of propulsor motors, other than the single propulsor motor, while the synchronization circuit synchronizes the single propulsor motor with the AC generator. 
 
     
     
       11. The electric propulsion system of  claim 1 , wherein the control unit is further configured to maintain synchronicity between the single propulsor motor and the AC generator by disengaging the synchronization circuit from the single propulsor motor after the synchronization circuit synchronizes the single propulsor motor with the AC generator. 
     
     
       12. The electric propulsion system of  claim 1 , wherein the control unit is configured to determine that the single propulsor motor is not synchronized with the AC generator by at least determining that a speed of the single propulsor motor does not satisfy an operating speed threshold of the plurality of motors. 
     
     
       13. The electric propulsion system of  claim 1 , wherein the control unit is configured to determine that the single propulsor motor is not synchronized with the AC generator by at least receiving information from the single propulsor motor that indicates the single propulsor motor has fallen out-of-synch with the AC generator. 
     
     
       14. The electric propulsion system of  claim 1 , wherein the synchronization circuit is sized to be able to synchronize only the single propulsor motor from the plurality of propulsor motors at a time. 
     
     
       15. An electric propulsion system comprising:
 means for determining that a single propulsor motor from a bank of propulsor motors is not synchronized with a generator; 
 means for disengaging only the single propulsor motor from the generator; 
 means for engaging only the single propulsor motor with a synchronization circuit shared by the bank of propulsor motors; 
 means for determining that the single propulsor motor is synchronized with the generator; 
 means for engaging the single propulsor motor with the generator; and 
 means for disengaging the single propulsor motor from the synchronization circuit. 
 
     
     
       16. A method comprising:
 determining whether a single propulsor motor from a bank of propulsor motors of an electric propulsion system is not synchronized with a generator of the electric propulsion system; 
 responsive to determining that the single propulsor motor is not synchronized with the generator, engaging, by a control unit, only the single propulsor motor with a synchronization circuit of the electric propulsion system that is shared by the bank of propulsor motors; and 
 responsive to determining that the single propulsor motor is synchronized with the generator, disengaging, by the control unit, the single propulsor motor from the synchronization circuit. 
 
     
     
       17. The method of  claim 16 , further comprising:
 further responsive to determining that the single propulsor motor from the bank of propulsor motors is not synchronized with the generator and prior to engaging only the single propulsor motor with the synchronization circuit, disengaging, by the control unit, only the single propulsor motor from the generator; and 
 further responsive to determining that the single propulsor motor is synchronized with the generator, engaging, by the control unit, the single propulsor motor with the generator before disengaging the single propulsor motor from the synchronization circuit. 
 
     
     
       18. The method of  claim 16 , further comprising:
 determining, by the control unit, a speed associated with the single propulsor motor; 
 determining, by the control unit, that the single propulsor motor is synchronized with the generator in response to determining that the speed satisfies an operating speed threshold of the bank of propulsor motors; and 
 determining, by the control unit, that the single propulsor motor is not synchronized with the generator in response to determining that the frequency, voltage and phase do not satisfy the operating speed threshold of the bank of propulsor motors. 
 
     
     
       19. The method of  claim 18 , wherein determining the speed associated with the single propulsor motor comprises inferring the speed based on a current level associated with the single propulsor motor. 
     
     
       20. The method of  claim 16 , wherein engaging only the single propulsor motor with the synchronization circuit comprises configuring a plurality of isolation devices of the electric propulsion system to electrically isolate the single propulsor motor from the generator while maintaining electrical coupling between the generator and each of the propulsor motors from the bank of propulsor motors, other than the single propulsor motor.